The present invention relates flat tubes and heat exchangers made therefrom.
A flat tube and a heat exchanger with a flat tube block are described in the European patent publication EP 0 659 500 A1. In order to manufacture this type of flat tube, a straight flat-tube blank is first bent out in U-shape from the flat-tube plane until the flat-tube arms extend parallel to one another, after which these arms are respectively twisted by 90xc2x0 relative to the U-bend region. The flat tube which results from this operation therefore has two flat-tube sections, which are located in one plane and whose outlets are located at the same end, opposite to the reversal-bend section. Along the reversal-bend section, the angle which is enclosed between the flat-tube transverse center line and the plane in which the straight tube arms are located first increases, over one torsion region, from zero to the value of 90xc2x0 present at the apex end of the reversal-bend section and then decreases, over the other torsion region, back to 0xc2x0. In the apex region of the reversal-bend section, therefore, the amount by which the flat tube extends at right angles to the plane of the flat tube arms corresponds to the flat-tube width. In the heat-exchanger tube block, a plurality of such flat tubes are stacked one above the other in the direction at right angles to the plane of the straight flat-tube arms, so that it is necessary to keep the stacking distance between the straight tube arms of adjacent flat tubes greater than the flat-tube width because the amount by which the reversal-bend sections extend corresponds, in this direction, to the width of the flat tubes. The tube-block flat tubes, which are configured in single-chamber design, open into a collector which is arranged at one end of the tube block, which is subdivided by a longitudinal partition into two collector spaces and into which the flat tubes respectively open at one or other of their ends.
The German patent publication DE 39 36 109 A1 shows a heat exchanger with a tube block which is formed from a stack of round tubes, which are configured in U-shape, where a single reversal-bend section is used, or as a tube serpentine, where a plurality of sequential reversal-bend sections is used, the tube sections extending in a straight line and flattened between the reversal-bend sections. The flattened tube sections of the round tube are located transversely offset in one plane, whereas the reversal-bend section or sections, and the two tube end regions which open at the same end, retain the circular tube cross section. The flattening of the straight tube sections takes place by means of flat presses. The round end regions of the tubes open into a collector space or a distributor space, which are respectively formed by a collector tube and distributor tube or by a longitudinally divided collector box and distributor box. The distance between the flattened tube sections of adjacent tubes in the tube-block stack must necessarily be greater than the diameter of the round tubes used.
The U.S. Pat. No. 3,416,600 shows a heat exchanger of serpentine design which contains a tube/rib block with a plurality of serpentine-shaped twisted flat tubes, which are stacked one above the other in the block in the serpentine winding direction. The tube/rib block has a U-shape in the plane at right angles to the tube stacking direction, each serpentine flat-tube opening at one end, at each of the two free U-ends, into a respective collector tube extending parallel to the stacking direction. In this arrangement, the two ends of each flat tube are twisted by 90xc2x0 and the two collector tubes have corresponding penetration slots, which are at a distance from one another and in which the twisted tube ends are accepted in a fluid-tight manner. In addition, each serpentine flat tube is twisted in a lateral block region in the vicinity of a serpentine winding by 180xc2x0 so that one part of each flow duct of the multichamber flat tubes used faces toward a front side of the block and the other part faces toward the opposite, rear side of the block.
The French patent publication FR 2 712 966 A1 shows a heat exchanger with a tube/rib block which contains a stack of straight multichamber flat tubes, which are twisted at their two opposite ends by an angle, to a maximum of 45xc2x0, and open into associated collector tubes, which are provided at their periphery with corresponding sequential oblique slots spaced apart in the longitudinal direction of the collector tube.
The present invention is based, as a solution to a technical problem, on the provision of a flat tube of the type described above, that can be manufactured relatively simply and which is suitable for the construction of very pressure-resistant heat exchangers with a small internal volume and a high heat transfer efficiency, and is based on the provision of a heat exchanger built up from such flat tubes.
The flat tube and heat exchanger according to the present invention solve this problem by the provision of a flat tube with a reversal-bend section that is formed in such a way that, in this region, an angle of 45xc2x0 is enclosed, as a maximum, between the transverse center line of the flat tube and the planes which are parallel to a longitudinal direction and a transverse direction and are at right angles to a stacking direction. The longitudinal direction is then defined by the course of the longitudinal center lines of the flat-tube sections, whereas the stacking direction designates that direction in which a plurality of flat tubes are arranged sequentially in the formation of a heat-exchanger tube block. The transverse direction represents the direction at right angles to this longitudinal direction and to the stacking direction thus defined. The transverse direction so defined is generally parallel to the transverse center line direction of the flat-tube sections. This, however, is not imperative because, as an alternative, the flat-tube sections can also, if required, be inclined relative to this transverse direction.
This design of the reversal-bend section in accordance with the invention achieves the effect that its extent in the stacking direction can be kept markedly less than the flat-tube width. It is not, in consequence, necessary to keep the intermediate spaces between adjacent flat tubes as large as or larger than the flat-tube width when a tube block is built up in stack form from these flat tubes. On the contrary, the intermediate spaces can be markedly narrower, which favors the manufacture of a compact and pressure-resistant heat exchanger. In addition, the reversal-bend section can be realized by means of relatively simple tube bending procedures. In these procedures, the flat tube can be bent round once or more in this manner, during which procedure its depth (front to back) extent, i.e. its extent in the transverse direction as defined above, is increased each time it is bent round. By this means, an arbitrarily deep (front to back) tube block, i.e. one which extends in the transverse direction, can be formed with relatively narrow, pressure-resistant flat tubes, this transverse or depth (front to back) direction usually representing that direction in which a medium to be cooled or heated is led through the heat exchanger past the flat-tube surfaces on the outside. In order to improve the heat transfer, additional heat conducting ribs are then usually provided between the tube-block sections that follow one another in the stacking direction. Because, as stated, the tube intermediate spaces can be kept very narrow, the heat-conducting corrugated ribs employed can also be correspondingly low, which likewise improves the compactness and stability of a tube/rib block formed in this way.
The flat tube is bent round in such a way that the flat-tube sections connected by means of a respective reversal-bend section are located in the same longitudinal plane or in different longitudinal planes which are parallel to one another or are inclined relative to one another by a specifiable angle of tilt and, in fact, preferably with a mutual distance apart in the transverse direction between 0.2 mm and 20 mm in each case. When flat tubes are used which have been bent around once in this way, it is then possible to form a tube block with a depth (front to back) which corresponds to twice the flat-tube width plus the stated distance apart of the flat-tube sections. When flat tubes have been bent around in this way a plurality of times, the tube-block depth (front to back) increases per reversal-bend section by the flat-tube width plus the stated transverse distance apart of the flat-tube sections. If the transverse distance apart is retained, corresponding gaps are formed in a tube block built up from such flat tubes and this, for example, facilitates the precipitation of condensate water in the application to an evaporator for a motor vehicle air-conditioning system. In certain cases, heat-conducting ribs which are provided can, if required, extend continuously over the complete tube-block depth (front to back) and somewhat beyond it.
A serpentine flat tube is formed by at least one of the two flat-tube parts connected by means of a reversal-bend section being bent to form a tube serpentine in the stacking direction, i.e. it consists of serpentine windings which follow one another in the stacking direction. By means of flat tubes designed in this way, it is possible to construct a so-called serpentine heat exchanger with any given number of serpentine block parts following one another in the depth (front to back) direction.
The flat tube further can be configured with the opening ends located at the same end or at opposite ends, at least one end (preferably both ends) being twisted relative to the abutting central region. Toward the opening end, the flat-tube transverse center line is rotated by means of this twisting, toward the stacking direction, so that the amount by which the flat-tube ends extend in the transverse direction can be kept smaller than the flat-tube width. The twisting takes place by 90xc2x0, as a maximum, so that in the case of flat-tube sections extending at right angles to the stacking direction, the tube ends are then located parallel to the stacking direction and their extent in the transverse direction is only as large as the flat-tube thickness. This permits a comparatively narrow arrangement, in the depth (front to back) direction of a tube block constructed in this way, of associated collector and distributor ducts which extend in the stacking direction at the relevant tube block end.
The heat exchanger in accordance with the present invention features the use of one or a plurality of the flat tubes according to the invention in the construction of a corresponding tube block, which has the properties and advantages mentioned above for such a tube-block construction. In particular, this permits the manufacture of a compact, highly pressure-resistant evaporator of relatively low weight, low internal volume and with good condensate water separation for an air-conditioning system of a motor vehicle, with multichamber flat tubes being preferably employed. The heat exchanger can be manufactured in either single-layer construction, in which the flat-tube sections consist of a flat, straight tube section between two reversal-bend sections or between one reversal-bend section and a flat-tube end, or in serpentine construction in which these flat-tube sections are bent to form a tube serpentine.
Such a heat exchanger further can be configured with the tube ends of the flat tubes used, and therefore also the associated collector and distributor ducts which, for simplicity, are uniformly designated as collector ducts below, located on opposite tube-block ends. The collector ducts can then each be formed from one collector box or collector tube, which extend on the relevant tube-block end along the stacking direction, also designated the block height direction, and which are used for the parallel supply and removal of the temperature-control medium led through the inside of the tube to the or from the individual flat tubes.
In a further configuration of the invention, which configuration is an alternative to that above, the flat-tube ends all open at the same tube-block end. Because of the design of the flat tubes, the two tube ends of a single flat tube are then offset relative to one another in the block depth (front to back) direction, so that two collector ducts correspondingly adjacent to one another in the block depth (front to back) direction can be associated with them. The supply and removal of the temperature-control medium, which is led through the inside of the tubes, takes place correspondingly at the same heat exchanger end.
In further embodiment of this heat exchanger type with two adjacent collector ducts at the same tube-block end, provision is made to form these collector ducts by two separate collector tubes or collector boxes, uniformly designated below, for simplicity, as collector tubes, or by a common collector tube. The latter can be manufactured by subdividing an initially uniform collector tube internal space by a longitudinal partition into the two collector ducts, or by the collector tube being manufactured as an extruded tube profile with two separate hollow chambers forming the collector ducts.
Further, at least one of the two collector tubes or at least one of the two hollow chambers of a longitudinally divided collector tube is subdivided by transverse partitions into a plurality of collector ducts separated from one another in the block height direction. By this means, a serial through-flow in groups of the flat tubes in the tube block is achieved because the temperature-control medium supplied to the tube block via a first collector duct of the transversely divided collector tube or of the transversely divided hollow chamber is initially fed only into the part of the all the flat tubes which opens there. The collector duct into which the other tube end of this part of the flat tubes opens then functions as a reversal duct, in which the temperature-control medium from the flat tubes opening there is deflected into a further part of all the flat tubes likewise which opens there with one end. The number and position of the transverse partitions determine the subdivision of the flat tubes into groups (through which flow takes place in series) of flat tubes (through which flow takes place in parallel).